1. Field of Invention
The present invention relates to a mask and a method for forming patterns by using the same. More particularly, the present invention relates to a mask for improving proximity effects for the patterns and the pattern forming method by using the same.
2. Description of Related Art
In the conventional photolithography process, strip structures in parallel are in general formed by transferring strip patterns to the photoresist layer by using the mask having the strip patterns and then etching the underlying layer through the patterned photoresist layer. However, the outermost strip patterns of the patterns formed in the photoresist layer usually have problems of non-uniform aerial image and contrast or photoresist loss, thus causing undesirable impacts on the subsequently formed strip structures.
In order to solve the above problems, a dummy pattern is formed outside the outermost strip patterns of the patterns in the mask. When patterns are transferring to the photoresist layer, the proximity effects and photoresist loss occur in the dummy pattern. Therefore, the strip patterns between the outermost dummy patterns can be formed properly. Alternatively, a plurality of scattering bars is formed outside the outermost strip patterns of the patterns in the mask. Similarly, the outermost strip patterns can be free of proximity effects during the pattern transfer to the photoresist layer.
However, for the aforementioned method of forming dummy patterns in the mask, dummy patterns will be transferred to the photoresist layer or further to the wafers. Hence, the layout design of the wafer has to take the dummy patterns into consideration, which significantly reduces the workable area of the wafer.
For the method of using scattering bars, reliable strip patterns can be obtained by disposing additional scattering bars in the mask, which consumes much area of the mask and increases the layout budget of the mask. Moreover, certain issues such as non-uniform aerial image and contrast during defocus can not be improved by the use of scattering bars.